In many electronic devices such as personal digital assistants (PDAs), radiotelephones, handheld computers, and/or laptop/notebook computers, a liquid crystal display is used as an output user interface to provide information visually. A Thin Film Transistor Liquid Crystal Display (TFT LCD), for example, has a sandwich-like structure with liquid crystal between two glass substrates. A first TFT glass substrate includes thereon a thin film transistor for each pixel of the display, and a second color filter glass substrate includes a color filter to generate color. A liquid crystal material between the two glass substrates moves in accordance with differences in voltage between the color filter glass substrate and the TFT glass substrate. A backlight transmits illumination through the liquid crystal display, and an attenuation of illumination transmitted through each pixel of the display is determined by an amount of movement of the liquid crystal material at that pixel, and a size of a transmissive area of a pixel.
Light sensors for displays are discussed, for example, in U.S. Pat. No. 5,831,693 (the '693 patent), and in U.S. Pat. No. 5,384,577 (the '577 patent), the disclosures of which are hereby incorporated herein in their entirety by reference. The '693 patent discusses self adjusting a display luminance of an active matrix liquid crystal display panel according to ambient lighting. More particularly, at least one photodiode is fabricated on a lower glass substrate using effectively the same process steps as those used to fabricate the display panel. The '577 patent discusses a combination display backlight and light sensor.